Method and apparatus for regulating the fluid flow rate to and preventing over-pressurization of a balloon catheter

ABSTRACT

The invention relates to an apparatus and method for limiting the pressure of inflation fluid injected into a drug delivery catheter balloon, while permitting continuous and uninterrupted flow of such fluid to the balloon. The apparatus includes an elongated hollow housing having a fluid entrance, a fluid exit and a bore extending therebetween which forms an interconnecting chamber and passageway. A piston and piston shaft assembly is disposed inside the housing and is longitudinally movable within the chamber. The piston and piston shaft assembly is biased against the fluid pressure of the fluid entering the housing by a spring. The piston shaft has a distal end which extends toward the passageway inlet. As the incoming fluid pressure increases and approaches the predetermined maximum pressure level of the apparatus, the piston shaft distal end moves within the chamber against the biasing force of the spring toward a position adjacent the passageway inlet. When the incoming fluid pressure reaches and exceeds the predetermined maximum pressure level, the piston shaft distal end enters and extends into the passageway, thereby forming an annulus within the passageway. The annulus functions to restrict the flow rate and limit the pressure of the fluid exiting the housing and entering the catheter balloon.

FIELD OF INVENTION

The present invention relates to catheter techniques and devices fordelivering therapeutic and/or diagnostic agents to a site within apatient's vasculature or bodily organ. More particularly, the presentinvention relates to a method and apparatus for regulating the flow rateof a fluid agent to and preventing the over-pressurization of aperforated drug delivery balloon catheter.

BACKGROUND OF THE INVENTION

Various drug delivery catheter designs and procedures have beendeveloped over the last several years for use in a wide range of medicalapplications. One such design and procedure involves the delivery oftherapeutic and/or diagnostic agents to a localized area of a patient'svasculature through the use of a perforated balloon catheter. Typically,such prior art drug delivery catheters include a balloon having aplurality of apertures spaced about its surface located at the distalend of the catheter. The interior of the balloon is in fluidcommunication with an inflation lumen which extends throughout thelength of the catheter. After the balloon has been placed within thepatient's vasculature or other bodily organ at the position of thetreatment site, inflation fluid comprising a therapeutic or diagnosticagent is injected under pressure through the inflation lumen and intothe balloon. The pressurized inflation fluid fills the balloon, migratesthrough the apertures in the balloon wall and penetrates the tissue wallat the treatment site. The balloon apertures are sized such that theballoon remains pressure-inflated despite the flow of the fluid agentthrough the apertures in the balloon wall.

Perforated balloon drug delivery catheters such as the one describedabove are capable of delivering a wide range of therapeutic and/ordiagnostic agents. For example, perforated balloon catheters aredesigned for use in conjunction with angioplasty dilatation for treatingthe site of an opened atherosclerotic lesion or stenosis with atherapeutic agent such as heparin to inhibit unregulated smooth musclecell proliferation and prevent restenosis. Alternatively, perforatedballoon catheters may be used to deliver a drug or agent to dissolve astenosis in an effort to avoid use of angioplasty or atherectomyprocedures, or to deliver a thrombolytic agent to dissolve a clot at thelesion site. In addition, perforated balloon catheters also may be usedto administer antibiotics or anesthetics directly to the treatment siteprior to removal of the catheter. Other agents which may be administeredthrough perforated balloon catheters include steroids for suppressinginflammation in a localized tissue site, anti-neoplastic for treating atumor site, chemotherapeutics or any desired mixture of individualpharmaceuticals.

Despite the development of this broad range of applications forperforated balloon drug delivery catheters, improvement in the controlof the infusion of the inflation fluid to the treatment site isdesirable. Typically, the inflation fluid is manually injected into theperforated drug delivery balloon catheter by means of a syringe devicecomprising a syringe plunger and barrel. Accordingly, the rate ofinfusion of the inflation fluid to the treatment site depends on thepressure applied on the syringe plunger by the physician when expellingthe inflation fluid from the syringe device. It has been found that theprecise control of the pressure at which the inflation fluid is injectedinto the catheter is important, thus requiring great skill on the partof the administering physician. For example, the exertion of excessivepressure on the syringe plunger by the physician may result inover-pressurization of the inflation fluid within the balloon, suchover-pressurization may cause high velocity jetting of the inflationfluid through the balloon apertures and possible trauma to the interiorwalls of the patient's vasculature.

Moreover, it has been found that the use of a pressure gauge to assistthe physician in monitoring the pressure at which the inflation fluid isinjected into the catheter does not assure precise control of theinfusion of inflation fluid to the treatment site. For example, a dropin the pressure indicated on the pressure gauge generally causes thephysician to accelerate the movement of the syringe plunger into thesyringe barrel, thereby resulting in a pressure spike. Any such pressurespike may result in over-pressurization of the balloon and,consequently, possible high velocity jetting of inflation fluid throughthe balloon apertures.

In an effort to prevent high velocity jetting resulting fromover-pressurization of the fluid within the perforated balloon, variousforms of shut-off valves have been developed for limiting the pressureof the inflation fluid within the balloon. However, because these valvesare designed to remain closed when the inflation fluid pressure exceedsa predetermined maximum allowable pressure, the flow of inflation fluidthrough the catheter to the treatment site may be discontinued for anindefinite period of time. It is understood that leaving the catheter inthe patient's vasculature for any such prolonged period of time canadversely effect the patient's blood flow and thereby complicate theprocedure. Moreover, the efficacy of the procedure may be compromised bya prolonged and an interrupted application of the drug to the treatmentsite.

Therefore, there exists a need for a method and apparatus for limitingthe pressure of the inflation fluid within the perforated balloon so asto prevent high velocity jetting of the fluid through the balloon wall,and also permitting the continuous and uninterrupted flow of the drug tothe treatment site.

OBJECTS AND SUMMARY OF THE INVENTION

In accordance with the present invention, an apparatus and method areprovided for limiting the pressure of inflation fluid injected into aperforated drug delivery catheter balloon while permitting a continuousand uninterrupted flow of such inflation fluid to the balloon. Theinvention relates to an apparatus and method for creating an annuluswithin the flow path between the pressurized source of inflation fluidand the catheter balloon when the pressure of the inflation fluidexceeds the predetermined maximum pressure level of the apparatus. Theannulus functions to restrict the flow rate and limit the pressure ofthe inflation fluid which flows to the catheter balloon.

Generally, the apparatus of the present invention comprises an elongatedhollow housing which is coupled in flow communication between thepressurized source of inflation fluid and the catheter balloon. Theinterior of the housing forms an interconnecting chamber and passageway.The chamber is designed to receive a piston and piston shaft assemblywhich is biased longitudinally within the chamber under the opposingforces exerted by the pressurized inflation fluid and a spring disposedwithin the chamber. The piston shaft includes a distal end which extendstoward the passageway inlet. As the pressure of the inflation fluidincreases and approaches the predetermined maximum pressure level of thepresent device, the piston shaft distal end moves toward the passagewayinlet. When the pressure of the inflation fluid exceeds thepredetermined maximum pressure level of the device, the piston shaftdistal end enters and extends into the passageway and thereby creates anannulus within the passageway. The annulus has the effect of restrictingthe flow rate and limiting the pressure of inflation fluid passingthrough the device and into the balloon. A further aspect of theinvention includes means for adjusting the maximum pressure level of theapparatus.

It is, therefore, a principal object of the present invention to providea method and apparatus for use with a perforated drug delivery ballooncatheter to prevent the over-pressurization of the balloon and providethe continuous and uninterrupted flow of the drug agent to the treatmentsite.

It is a further object of the present invention to provide an apparatusfor use in a drug delivery balloon catheter which may be adjusted forlocalized delivery of therapeutic and/or diagnostic agents havingdifferent fluid characteristics.

It is also an object of the present invention to provide an apparatusfor use in a drug delivery balloon catheter to enable efficient drugdelivery and to prevent the waste of excess portions of such druginjected into the catheter.

Objects and advantages of the invention are set forth in part above andin part below. In addition, these and other objects and advantages ofthe invention will become apparent herefrom, or may be appreciated bypractice with the invention, the same being realized and attained bymeans of instrumentalities, combinations and methods pointed out in theappended claims. Accordingly, the present invention resides in the novelparts, constructions, arrangements, improvements, methods and stepsherein shown and described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing showing a plan view of a balloon catheteremploying the over-inflation protection apparatus according to thepresent invention;

FIG. 2 is a longitudinal cross-sectional view of an embodiment of abasic form of the present invention wherein the piston and piston shaftare in open positions;

FIG. 3 is a longitudinal cross-sectional view of the embodiment of thepresent invention shown in FIG. 2 wherein the piston shaft distal end isapproaching a flow regulating position;

FIG. 4 is a longitudinal cross-sectional view of the embodiment of thepresent invention shown in FIG. 2 wherein the piston shaft distal end isin a flow regulating position;

FIG. 5 is a longitudinal cross-sectional view of a preferred embodimentof the present invention which provides for varying the predeterminedmaximum pressure level of the device;

FIG. 6 is a longitudinal cross-sectional view of the preferredembodiment shown in FIG. 5 wherein the longitudinal position of thepiston shaft distal end has been adjusted relative to the passagewayinlet; and

FIG. 7 is a sectional view taken along line 7--7 of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring generally to the embodiments of the invention shown in theaccompanying drawings, wherein like reference numbers refer to likeparts throughout the various views, the basic principles of the broadestaspects of the invention can be appreciated from FIGS. 1-4.

As shown in FIG. 1, a drug delivery balloon catheter 10 generallycomprises a catheter tube 12 having a perforated balloon 16 located atits distal end. Catheter tube 12 further includes at least one inflationlumen which extends longitudinally throughout essentially the entirelength of the catheter tube and provides flow communication between theinterior of the balloon 16 and a syringe or other pressure infusiondevice coupled to an injection port 14 located at the proximal end ofcatheter tube 12.

In accordance with one embodiment of the present invention, the device18 is coupled in flow communication between injection port 14 and thesource of pressurized inflation fluid (not shown). In this arrangement,the fluid agent is introduced into the device 18 under pressure via asyringe prior to entering injection port 14 and traveling through theinflation lumen to balloon 16.

The present invention, as illustrated in a basic form in FIG. 2,provides means for controlling the flow rate of the fluid agent andregulating the pressurization of the balloon during a catheterizationprocedure. As here embodied, the device of the present inventioncomprises an elongated hollow body having a cap 40 and housing 20.Housing 20 includes a bore extending throughout its length defining aninlet 23 at one end and a manifold outlet 24 at the opposite end,wherein the bore consists of two interconnecting sections havingdifferent diameters. A first section defining a chamber 30 extends frominlet 23 to annular shoulder 26. A second section having a smallerdiameter than the first section and defining a passageway 32 extendsfrom annular shoulder 26 to annular shoulder 28 formed at manifoldoutlet 24. Passageway 32 includes an inlet 34 in flow communication withchamber 30.

Cap 40 comprises a hollow tube which forms an inlet manifold 22 adaptedto receive pressurized fluid from a syringe, or any other pressurizedsource acceptable for use with a catheter device. As shown in FIG. 2,cap 40 is removably coupled to housing 20, such that manifold inlet 22is in flow communication with chamber 30 within housing 20. Cap 40 maybe coupled to housing 20 by any of several different means known in theart. For example, the inside surface of cap 40 between annular shoulder42 and outlet end 44 may be fitted with a screw thread which mates witha complementary screw thread fitted on the outside surface of housing 20adjacent inlet 23. Alternatively, it will also be understood that thehollow elongated body formed by housing 20 and cap 40 may bemanufactured as a single unit.

As further shown in FIG. 2, piston 50 is slidably received withinchamber 30, such that its front surface faces inlet 23 and its backsurface faces passageway inlet 34. Piston 50 is coupled at its backsurface to the proximal end 54 of piston shaft 52. Piston shaft 52 isdisposed longitudinally within chamber 30, having a distal end 56extending toward passageway inlet 34. The diameter of piston shaft 52 isdimensioned to be smaller than the diameter of passageway 32 such thatwhen piston shaft distal end 56 extends through inlet 34 and intopassageway 32 an annulus is formed which restricts the flow rate andpressure of fluid passing from chamber 30, into passageway 32 andthrough manifold outlet 24.

With reference to FIG. 2, piston 50 and piston shaft 52 are normallymaintained in an open position by the biasing force of helicalcompression spring 58, which encircles piston shaft 52 and is interposedbetween the back surface of piston 50 and annular shoulder 26. As willbe understood with reference to the operation of the present inventionas described below, the length and/or compression constant of spring 58,or the length of piston shaft 52 may be varied to provide a specificpredetermined maximum allowable pressure value for the device. It willbe understood that alternative devices for biasing piston 50 in anormally open position such as a compressible resilient membrane may besubstituted for spring 58.

Housing 20 is designed to permit the passage of fluid from manifoldinlet 22, through chamber 30 and passageway 32, and to manifold outlet24. To this end, piston 50 is disposed within chamber 30 such that fluidmay readily pass between the outer side surface of piston 50 and theinner wall of housing 20 which forms chamber 30. Alternatively, othermeans may be included for providing flow communication between manifoldinlet 22 and passageway inlet 34. For example, the outer periphery ofpiston 50 may include one or more ducts extending from the piston frontsurface to its back surface.

In operation, the device 18 is initially coupled at manifold inlet 22 toa syringe containing pressurized fluid agent and at manifold outlet 24to the injection port of a balloon catheter as shown in FIG. 1.Referring now to FIG. 2, prior to the introduction of the fluid agent,piston 50 and distal end 56 of piston shaft 52 are maintained in theirnormally-open positions under the biasing force exerted by spring 58.When the device is in this state, there is provided a continuous flowpath for the fluid agent to pass from manifold inlet 22, through chamber30 and passageway 32, and out manifold outlet 24.

After the balloon has been positioned across the treatment site withinthe patient's vasculature or other bodily organ, the fluid agent isinjected under pressure into manifold inlet 22. The fluid agent thentravels through chamber 30 and passageway 32, before entering theproximal end of the catheter lumen coupled to manifold outlet 24. Thefluid agent continues through the catheter lumen and into balloon 16where it migrates through the apertures in the balloon wall to thetreatment site. While passing through chamber 30 the inflation fluidexerts a force on the front surface of piston 50 urging the piston andconnected piston shaft 52 toward passageway inlet 34. It is understoodthat the force exerted on piston 50 by the fluid agent is directlyproportionate to the pressure under which the fluid agent is injectedinto manifold inlet 22. To this end, as the pressure of the inflationfluid within chamber 30 increases, piston 50 and piston shaft 52 willmove longitudinally within chamber 30 toward the passageway inlet 34until the force exerted by the fluid agent on piston 50 is inequilibrium with the counteracting force of compression spring 58.

Referring now to FIG. 3, as the pressure of fluid agent within chamber30 approaches the predetermined maximum allowable pressure level of thepresent invention, piston shaft distal end 56 will advance to a positionimmediately adjacent to passageway inlet 34. Furthermore, asdemonstrated in FIG. 4 when the pressure exerted by the fluid agent onpiston 50 reaches and/or exceeds the predetermined maximum pressurelevel, piston shaft distal end 56 enters passageway inlet 34, therebycreating an annulus within passageway 32 which limits the area throughwhich the inflation fluid may flow through passageway 32. The annulusformed within passageway 32 functions to restrict the flow rate of fluidthrough passageway 32 and to create a pressure drop across the length ofthe annulus. Should the pressure of the fluid agent further increasebeyond the predetermined maximum pressure value, piston shaft distal end56 will extend further into passageway 32 and increase the length of theannulus. It will be understood that the amount of the pressure dropacross the annulus is directly proportionate to the length of theannulus formed by piston shaft 52 within passageway 32. Thus, thegreater the length of the annulus formed within passageway 32, thegreater the amount of the pressure drop across the annulus. Moreover,the relative dimensions of piston shaft 52 and passageway 32 aredesigned such that the amount of the pressure drop across the annulus isequal to the amount to which the pressure of the fluid within chamber 30exceeds the predetermined maximum pressure level of the device. Thusensuring that the pressure of the inflation fluid passing throughpassageway 32 and into balloon 16 will never exceed the predeterminedmaximum allowable pressure for the device of the present invention.

Preferably, the present invention may be adapted to provide differentmaximum allowable pressures for the fluid agent passing through thedevice and into the catheter balloon. To this end, in a preferred formof the present invention the normally-open position of the piston shaftdistal end 56 may be adjusted relative to passageway inlet 34. It willbe understood that by positioning the piston shaft distal end 56 eithercloser or further from passageway inlet 34 one can vary the amount offluid pressure required to force piston shaft distal end 56 intopassageway 32.

One embodiment of this preferred form of the invention, as illustratedin FIG. 5, comprises an outer housing 20, inner housing 60 and cap 40.Outer housing 20 includes a bore extending longitudinally throughout itslength, forming an inlet 23 and a manifold outlet 24. The bore in theouter housing 20 consists of three interconnecting sections havingdifferent diameters. A first section and a second section define achamber 30 extending from inlet 23 to annular shoulder 26. The firstsection extends from inlet 23 to annular shoulder 25. The second sectionhas a smaller diameter than the first section and extends from annularshoulder 25 to annular shoulder 26. The third section has a smallerdiameter than the second section and defines a passageway 32 extendingfrom annular shoulder 26 to annular shoulder 28 formed at manifoldoutlet 24. Passageway 32 includes an inlet 34 in flow communication withchamber 30.

As further illustrated in FIG. 5, inner housing 60 is longitudinallydisposed within chamber 30 of outer housing 20. Inner housing 60includes a first section adjacent inlet end 62 and a second sectionadjacent outlet end 64, having outside diameters which generallycorrespond to the diameters of the first and second sections of chamber30, respectively. The first section of inner housing 60 extends frominlet end 62 to annular shoulder 63. Whereas, the second section extendsfrom annular shoulder 63 to outlet end 64.

According to this embodiment, inner housing 60 is adjustably coupledwithin outer housing 20 such that the longitudinal position of pistonshaft distal end 56 relative to passageway inlet 34 may be varied. Tothis end, the outside surface of the first section of inner housing 60is fitted with a screw thread which mates with a complementary screwthread fitted on the inside surface of the portion of outer housing 20that defines the first section of chamber 30. Thus, by rotating theouter housing relative to the inner housing the longitudinal position ofinner housing 60 may be adjustably disposed within outer housing 20 tovary the distance between piston shaft distal end 56 and passagewayinlet 34 when piston 50 and piston shaft 52 are in the normally openposition. FIGS. 5 and 6 illustrate the adjustable feature of thepreferred embodiment showing two different longitudinal positions forpiston shaft distal end 56 relative to passageway inlet 34 when thedevice is in a normally open position.

As described with reference to FIGS. 5 and 7, inner housing 60 includesa concentric cylindrical bore 66 extending throughout its length andhaving openings at the inlet end 62 and outlet end 64. In addition, theoutside perimeter of the inner housing wall includes one or more ducts70, extending from inlet end 62 to annular shoulder 63.

Referring now to FIG. 5, piston 50 is received into bore 66. Piston 50is coupled to the proximal end 54 of piston shaft 52. Piston shaft 52 isdisposed longitudinally within bore 66, having a distal end 56 extendingthrough an opening in outlet end 64. Piston 50 is normally maintained ina fully open position by the biasing force of helical compression spring58, which encircles piston shaft 52 and is interposed between the backsurface of piston 50 and shoulder 68 formed at the outlet end of bore66.

Cap 40 comprises a hollow tube which forms an inlet manifold 22 adaptedto receive pressurized fluid from a syringe, or any other pressurizedsource acceptable for use with a catheter device. As shown in FIG. 5,cap 40 is removably coupled to inner housing 60, such that the inletmanifold 22 is in flow communication with the inlet end of bore 66 andducts 70. Cap 40 may be coupled to inner housing 60 by any of severaldifferent means known in the art. For example, the inside surface of cap40 between annular shoulder 42 and outlet end 44 may be fitted with acomplementary screw thread fitted which mates with the screw thread onthe outside surface of the first section of the inner housing.

When the pressure of the inflation fluid is at or below the maximumallowable pressure selected, this embodiment of the present invention isdesigned to permit the flow of pressurized inflation fluid from manifoldinlet 22 to manifold outlet 24. To this end, the diameter of the secondsection of chamber 30 is dimensioned to be slightly larger than thediameter of second section of inner housing 60. Accordingly, when theinner housing 60 is engaged with the outer housing 20 and cap 40, theinflation fluid is designed to pass from manifold inlet 22, throughducts 70, into the space within chamber 30 between the outside surfaceof inner housing 60 and the inside surface of outer housing 20 beforeentering passageway 32.

Likewise, if the pressure of the inflation fluid entering manifold inlet22 exceeds the maximum allowable pressure, the invention is designed tosimultaneously restrict the flow and limit the pressure of inflationfluid traveling through passageway 32 and into the catheter. To thisend, passageway 32 is dimensioned to have a cross-sectional diameterslightly larger than the cross-sectional diameter of piston shaft 52,such that an annulus is formed when the distal end 56 of piston shaft 52extends into passageway 32.

In operation, the preferred embodiment shown in FIGS. 5 and 7 functionsin generally the same manner as described above with respect to thebasic embodiment shown in FIGS. 2-4. However, prior to the injection ofinflation fluid the preferred embodiment of FIGS. 5 and 7 may beadjusted to vary the maximum allowable pressure of inflation fluid whichmay pass through the device and into the catheter balloon.

While only a few embodiments have been illustrated and described inconnection with the present invention, various modifications and changesin the apparatus will become apparent to those skilled in the art. Allsuch modifications or changes falling within the scope of the claims areintended to be included therein.

We claim:
 1. An apparatus for limiting the pressure and regulating theflow of inflation fluid entering a catheter balloon, comprising:(a) ahousing having an inlet port, an outlet port and a bore extendinglongitudinally throughout providing flow communication between the inletport and the outlet port, wherein the bore forms a chamber adjacent theinlet port having a diameter and a passageway adjacent the outlet porthaving a smaller diameter than the chamber diameter; (b) a pistonlongitudinally movable within the chamber having a front surface in flowcommunication with the inlet port; (c) biasing means disposed within thechamber for biasing the piston against the force exerted by pressurizedfluid entering the inlet port, such that as the pressure of the fluidpassing through the inlet port and into the chamber variably increasesto a predetermined maximum pressure level, the piston moves within thechamber in a direction opposite the biasing force; (d) a piston shafthaving a proximal end coupled to a back surface of the piston and adistal end extending toward the passageway inlet, such that when thepressure of the fluid entering the inlet port exceeds a predeterminedmaximum pressure level the piston shaft distal end enters the passagewayinlet and creates an annulus within the passageway.
 2. The apparatusaccording to claim 1, wherein the longitudinal position of the pistonshaft distal end may be adjusted within the chamber relative to thepassageway inlet when the piston shaft is in a normally-open position.3. The apparatus according to claim 1, wherein the biasing meanscomprises a spring.
 4. The apparatus according to claim 1, wherein thehousing comprises a body portion and a removable cap.
 5. A apparatus forlimiting the pressure and regulating the flow of inflation fluidentering a catheter balloon, comprising:(a) an outer housing having aninlet port, an outlet port and a bore extending longitudinallythroughout providing flow communication between the inlet port and theoutlet port, wherein the bore forms a chamber adjacent the inlet porthaving a diameter and a passageway adjacent the outlet port having asmaller diameter than the chamber diameter; (b) an inner housingdisposed within the outer housing having a bore extending longitudinallythroughout forming a hollow cylinder with an inlet in flow communicationwith the outer housing inlet port and an outlet in flow communicationwith the outer housing chamber; (c) means for providing flowcommunication for inflation fluid between the outer housing inlet portand the passageway inlet; (d) a piston longitudinally movable within thecylinder having a front surface in flow communication with the outerhousing inlet port; (e) biasing means disposed within the hollowcylinder for biasing the piston against the force exerted by thepressurized fluid entering the inner housing inlet, such that as thepressure of the fluid passing through the outer housing inlet port andinto the inner housing inlet variable increases to a predeterminedlevel, the piston moves within the hollow cylinder in a directionopposite the force exerted by the biasing means; (f) a piston shafthaving a proximal end coupled to a back surface of the piston and adistal end extending through the cylinder and toward the passagewayinlet, such that when the pressure of the fluid entering the inlet portexceeds a predetermined maximum pressure level the piston shaft distalend enters the passageway inlet and creates an annulus within thepassageway.
 6. The apparatus according to claim 5, wherein thelongitudinal position of the inner housing relative to the outer housingmay be adjusted such that the distance between the piston shaft distalend and the passageway inlet may be varied when the piston shaft is in anormally-open position.
 7. The apparatus according to claim 5, whereinthe biasing means comprises a spring.
 8. The apparatus according toclaim 5, wherein the means for providing flow communication of inflationfluid between the outer housing inlet port and the passageway inletcomprises a plurality of ducts extending longitudinally throughout thelength of the inner housing wall.
 9. The apparatus according to claim 5,wherein the outer housing comprises a body portion and a removable cap.10. An apparatus for limiting the pressure and regulating the flow ofinflation fluid entering a catheter balloon, comprising:(a) an outerhousing having a inlet end, an outlet port and a bore extendinglongitudinally throughout providing flow communication between the inletend and the outlet port, wherein the bore forms a chamber adjacent theouter housing inlet end having a diameter and a passageway adjacent theoutlet port having a diameter smaller than the chamber diameter; (b) aninner housing disposed within the outer housing chamber, having a boreextending longitudinally throughout forming a hollow cylinder with aninlet and an outlet in flow communication with the passageway inlet; (c)a cap having an inlet port, an outlet end and a bore extendinglongitudinally throughout providing flow communication between the inletport and the outlet end, wherein the cap outlet end is coupled to theinlet end of the inner housing such that the inlet port is in flowcommunication with the inner housing inlet; (d) means for providing flowcommunication for inflation fluid between the inlet port and thepassageway inlet; (e) a piston longitudinally movable within the innerhousing hollow cylinder and having a front surface in flow communicationwith the inlet port; (f) biasing means disposed within the hollowcylinder for biasing the piston against the pressure of the fluidentering from the inlet end of the inner housing hollow cylinder, suchthat as the pressure of the fluid passing through the inlet port andinto the inner housing inlet variably increases to a predeterminedlevel, the piston moves within the inner housing cylinder in a directionopposite the force exerted by the biasing means; and (g) a piston shaftcoupled at a proximal end to a back surface of the piston and having adistal end extending through the inner housing hollow cylinder and intothe outer housing chamber, such that when the pressure of the fluidentering the inlet port exceeds a predetermined maximum pressure levelthe piston shaft distal end enters the passageway inlet and creates anannulus within the passageway.
 11. The apparatus according to claim 10,wherein the inner housing is adjustably coupled to the outer housingsuch that the longitudinal position of the piston shaft distal endrelative to the passageway inlet may be varied.
 12. The apparatusaccording to claim 10, wherein the biasing means is a spring.
 13. Theapparatus according to claim 10, wherein the means for providing flowcommunication of inflation fluid between the outer housing inlet portand the passageway inlet comprises a plurality of ducts extendinglongitudinally throughout the length of the inner housing wall.
 14. Amethod for limiting the pressure and providing an uninterrupted flow offluid passing from a source of pressurized fluid to a catheter balloon,comprising:(a) providing a passageway in flow communication between thesource of pressurized fluid and the catheter balloon; (b) passing fluidfrom the source of pressurized fluid through the passageway and into theballoon; and (c) forming an annulus within the passageway whichrestricts the flow rate of fluid passing through the passageway andcreates a pressure drop across the length of the annulus when thepressure of the fluid entering the passageway exceeds a predeterminedmaximum pressure level.
 15. The method according to claim 14, whereinthe annulus within the passageway is formed by disposing a shaft withinthe passageway, wherein the shaft has a smaller cross-sectional areathan the passageway.
 16. The method according to claim 15, wherein thepredetermined maximum pressure level may be varied.
 17. The methodaccording to claim 15, wherein the pressure drop across the length ofthe annulus is equal to the difference between the pressure of the fluidentering the passageway and the predetermined maximum pressure level.